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Every musical note has pitch, which corresponds to frequency of main tone. Modern musical scale has almost 100 pitches with frequences from approximately 30 hertz to 4,5 kilohertz. Neighbor notes frequences (C and C#, E and F) are always related as 2 in 1/12 power, so notes making an octave interval (=12 smallest called halftones) have frequences rated as 1:2. There are other scales, and program MUSTUNE contains info on some of them. Also there are always other frequency components sounding together with main tone. They are called harmonics and their frequences are whole numbers of main tone frequency. Their relative strength is specific for every music instrument. The program cuts recording into small pieces (see parameter TimeTick in README), applies frequency analysis (concatenating the pieces for bass notes). Spectrum received is multiplied on Equalizer curve. Then maximums are rounded to nearest notes and written to MIDI file. Nowdays investigations of more complex schemes are taking place, it seems that they will allow to differentiate musical instruments and make less errors. |
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